Atelopus varius
Encyclopedia
The Costa Rican Variable Harlequin Toad (Atelopus varius), also known as the clown frog, is a neo-tropical true toad from the family Bufonidae (Crump 1986). Once ranging from Costa Rica
to Panama
, A. varius is now listed as critically endangered and has been reduced to a single remnant population near Quepos, Costa Rica (rediscovered in 2003) and is presumed to be extinct in Panama (IUCN, personal correspondence 2007). Recent variation in air temperature, precipitation, stream flow patterns, and the subsequent spread of a pathogenic chytrid fungus (Batrachochytrium dendrobatidis
) linked to global climate change have been the leading cause of decline for A. varius (Lips et al. 2003 and Pounds et al. 2006). A. zeteki has been considered a subspecies
of A. varius, but is now generally considered a separate species (Savage, 2002).
, Costa Rica (personal correspondence 2007).
species, only entering the water during breeding season, relying on spray from streams for moisture (Pounds and Crump 1994).
The Costa Rican variable harlequin frog is slow moving and often remains in the same area for long periods of time. The conspicuous or aposematic coloration of A. varius likely serves as a warning to potential predators of the toxicity of the frog's integument which contains tetrodotoxin
, a potent neurotoxin
(Crump and Pounds 1985). Its main food source is small arthropod
s that are most abundant during the dry season (Crump 1988).
The only known predator of A. varius is a parasitic sarcophagid fly (Notochaeta bufonivora) which deposits its larvae on the surface of the frog's thigh. The larvae then proceed to burrow inside the frog and eat it from within (Pounds and Crump 1987). In addition, large land crabs have recently been observed attempting to prey on A. varius but it is unclear what, if any, effect this has on the population (personal correspondence 2007).
, Costa Rica revealed zero individuals where its population had previously peaked at 751 adults (Crump and Pounds 1985 and Pounds and Crump 1994). By 1996, A. varius was believed to be extinct throughout Costa Rica. However, subsequent surveys carried out by the rainmaker project in 2003 and 2005 rediscovered a population of the endangered frog on the Pacific coastal range near Quepos (IUCN). In Panama, mass mortality has drastically reduced populations of A. varius in recent years and it is now believed to be locally extinct (Lips 1999, personal correspondence 2007). At present only a single population of an estimated 60-95 individuals remains in an isolated location in Costa Rica (personal correspondence 2007).
Several theories related to changes in climatic patterns have been put forth to account for the rapid decline of A. varius. A trend toward rising temperatures across the tropics in the late 80s and early 90s has been implicated in the declines of multiple lizard
and amphibian
species including several Atelopus spp. (Pounds et al. 1999). More recently, an observed global decline in amphibian species
richness has been linked to an outbreak of the pathogenic chytrid fungus Batrachochytrium dendrobatidis
(Pounds et al. 2006). This pathogen can be transmitted between individuals through shed skin cells and is known to infect keratin
ized body surfaces where it can impair cutaneous respiration and osmoregulation
thus resulting in mortality (Pounds et al. 2006). Current attempts to preserve A. varius include a recently initiated captive breeding program as well as continued efforts to protect vital forest habitat (IUCN).
Recent testing indicates that the remaining population of A. varius is presently free of chytrid infection. In order to avoid future transmission, monitoring is carried out twice annually by a small group of researchers following strict decontamination protocols. Additionally, the persistence of A. varius is threatened by predation, habitat alteration, and the potentially detrimental effects of inbreeding
. Current conservation efforts consist of population and microclimate monitoring, genetic studies, and habitat protection. Although evidence suggests that the current population is reproductively active and relatively stable, the long-term prognosis for A. varius is uncertain (personal correspondence 2007).
Costa Rica
Costa Rica , officially the Republic of Costa Rica is a multilingual, multiethnic and multicultural country in Central America, bordered by Nicaragua to the north, Panama to the southeast, the Pacific Ocean to the west and the Caribbean Sea to the east....
to Panama
Panama
Panama , officially the Republic of Panama , is the southernmost country of Central America. Situated on the isthmus connecting North and South America, it is bordered by Costa Rica to the northwest, Colombia to the southeast, the Caribbean Sea to the north and the Pacific Ocean to the south. The...
, A. varius is now listed as critically endangered and has been reduced to a single remnant population near Quepos, Costa Rica (rediscovered in 2003) and is presumed to be extinct in Panama (IUCN, personal correspondence 2007). Recent variation in air temperature, precipitation, stream flow patterns, and the subsequent spread of a pathogenic chytrid fungus (Batrachochytrium dendrobatidis
Batrachochytrium dendrobatidis
Batrachochytrium dendrobatidis is a chytrid fungus that causes the disease chytridiomycosis. In the decade after it was first discovered in amphibians in 1998, the disease devastated amphibian populations around the world, in a global decline towards multiple extinctions, part of the Holocene...
) linked to global climate change have been the leading cause of decline for A. varius (Lips et al. 2003 and Pounds et al. 2006). A. zeteki has been considered a subspecies
Subspecies
Subspecies in biological classification, is either a taxonomic rank subordinate to species, ora taxonomic unit in that rank . A subspecies cannot be recognized in isolation: a species will either be recognized as having no subspecies at all or two or more, never just one...
of A. varius, but is now generally considered a separate species (Savage, 2002).
Geographic range
The historic range of A. varius stretched from the Pacific and Atlantic slopes of the Cordilleras de Tilaran mountain range in Costa Rica into western Panama. Suitable habitat includes both pre-montane and lower-montane zones as well as some lowland sites along rocky streams in hilly areas (ranging from 6 to 2000m in elevation) (Savage 1972). At present, A. varius is restricted to a single lowland site along a stream and small tributary on the Pacific coastal range near QueposQuepos
Quepos is a city in Puntarenas Province, Costa Rica. It is served by the Quepos-La Managua airport. It is located at around . It is home to approximately 14,000 people....
, Costa Rica (personal correspondence 2007).
Habitat and ecology
A. varius is a diurnal frog often found on rocks or in crevices along streams in humid lowland and montane forests (Crump and Pounds 1985). It is primarily a terrestrialTerrestrial animal
Terrestrial animals are animals that live predominantly or entirely on land , as compared with aquatic animals, which live predominantly or entirely in the water , or amphibians, which rely on a combination of aquatic and terrestrial habitats...
species, only entering the water during breeding season, relying on spray from streams for moisture (Pounds and Crump 1994).
The Costa Rican variable harlequin frog is slow moving and often remains in the same area for long periods of time. The conspicuous or aposematic coloration of A. varius likely serves as a warning to potential predators of the toxicity of the frog's integument which contains tetrodotoxin
Tetrodotoxin
Tetrodotoxin, also known as "tetrodox" and frequently abbreviated as TTX, sometimes colloquially referred to as "zombie powder" by those who practice Vodou, is a potent neurotoxin with no known antidote. There have been successful tests of a possible antidote in mice, but further tests must be...
, a potent neurotoxin
Neurotoxin
A neurotoxin is a toxin that acts specifically on nerve cells , usually by interacting with membrane proteins such as ion channels. Some sources are more general, and define the effect of neurotoxins as occurring at nerve tissue...
(Crump and Pounds 1985). Its main food source is small arthropod
Arthropod
An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...
s that are most abundant during the dry season (Crump 1988).
The only known predator of A. varius is a parasitic sarcophagid fly (Notochaeta bufonivora) which deposits its larvae on the surface of the frog's thigh. The larvae then proceed to burrow inside the frog and eat it from within (Pounds and Crump 1987). In addition, large land crabs have recently been observed attempting to prey on A. varius but it is unclear what, if any, effect this has on the population (personal correspondence 2007).
Conservation status
In recent decades, A. varius has become increasingly rare throughout its geographic range. The first incidence of its disappearance was recorded after a census conducted between 1990 and 1992 near MonteverdeMonteverde
Monteverde, Costa Rica is a small town in Puntarenas, Costa Rica. Located in the Cordillera de Tilarán, roughly a four hour drive from the Central Valley of Costa Rica, Monteverde is considered a major ecotourism destination in Costa Rica...
, Costa Rica revealed zero individuals where its population had previously peaked at 751 adults (Crump and Pounds 1985 and Pounds and Crump 1994). By 1996, A. varius was believed to be extinct throughout Costa Rica. However, subsequent surveys carried out by the rainmaker project in 2003 and 2005 rediscovered a population of the endangered frog on the Pacific coastal range near Quepos (IUCN). In Panama, mass mortality has drastically reduced populations of A. varius in recent years and it is now believed to be locally extinct (Lips 1999, personal correspondence 2007). At present only a single population of an estimated 60-95 individuals remains in an isolated location in Costa Rica (personal correspondence 2007).
Several theories related to changes in climatic patterns have been put forth to account for the rapid decline of A. varius. A trend toward rising temperatures across the tropics in the late 80s and early 90s has been implicated in the declines of multiple lizard
Lizard
Lizards are a widespread group of squamate reptiles, with nearly 3800 species, ranging across all continents except Antarctica as well as most oceanic island chains...
and amphibian
Amphibian
Amphibians , are a class of vertebrate animals including animals such as toads, frogs, caecilians, and salamanders. They are characterized as non-amniote ectothermic tetrapods...
species including several Atelopus spp. (Pounds et al. 1999). More recently, an observed global decline in amphibian species
Decline in amphibian populations
Dramatic declines in amphibian populations, including population crashes and mass localized extinctions, have been noted since the 1980s from locations all over the world...
richness has been linked to an outbreak of the pathogenic chytrid fungus Batrachochytrium dendrobatidis
Batrachochytrium dendrobatidis
Batrachochytrium dendrobatidis is a chytrid fungus that causes the disease chytridiomycosis. In the decade after it was first discovered in amphibians in 1998, the disease devastated amphibian populations around the world, in a global decline towards multiple extinctions, part of the Holocene...
(Pounds et al. 2006). This pathogen can be transmitted between individuals through shed skin cells and is known to infect keratin
Keratin
Keratin refers to a family of fibrous structural proteins. Keratin is the key of structural material making up the outer layer of human skin. It is also the key structural component of hair and nails...
ized body surfaces where it can impair cutaneous respiration and osmoregulation
Osmoregulation
Osmoregulation is the active regulation of the osmotic pressure of an organism's fluids to maintain the homeostasis of the organism's water content; that is it keeps the organism's fluids from becoming too diluted or too concentrated. Osmotic pressure is a measure of the tendency of water to move...
thus resulting in mortality (Pounds et al. 2006). Current attempts to preserve A. varius include a recently initiated captive breeding program as well as continued efforts to protect vital forest habitat (IUCN).
Recent testing indicates that the remaining population of A. varius is presently free of chytrid infection. In order to avoid future transmission, monitoring is carried out twice annually by a small group of researchers following strict decontamination protocols. Additionally, the persistence of A. varius is threatened by predation, habitat alteration, and the potentially detrimental effects of inbreeding
Inbreeding
Inbreeding is the reproduction from the mating of two genetically related parents. Inbreeding results in increased homozygosity, which can increase the chances of offspring being affected by recessive or deleterious traits. This generally leads to a decreased fitness of a population, which is...
. Current conservation efforts consist of population and microclimate monitoring, genetic studies, and habitat protection. Although evidence suggests that the current population is reproductively active and relatively stable, the long-term prognosis for A. varius is uncertain (personal correspondence 2007).